Circuit arrangement with half-bridge

Abstract

The invention relates to a circuit arrangement having a half-bridge arrangement comprising a first and a second switch (T 1 ;T 2 ), each switch (T 1 ;T 2 ) having, between its operating and reference electrodes, an internal diode (DB 1 ;DB 2 ), which is reverse-connected in parallel with the main current flow direction of the respective switch (T 1 ;T 2 ), and also an internal capacitance (C OSS 1 ;C OSS 2 ), a series diode (DS 1 ;DS 2 ) being arranged in series with the respective switch (T 1 ;T 2 ) in the main current flow direction in such a way that current can flow in the main current flow direction, and a freewheeling diode (DF 1 ;DF 2 ) being connected in parallel with the respective series circuit formed by the switch (T 1 ;T 2 ) and the series diode (DS 1 ;DS 2 ), and having a load circuit (L;RL), which has at least one inductive component (L) and is connected to the midpoint of the half-bridge arrangement. In order to reduce the failure rate of the series diodes (DS 1 ;DS 2 ), a load-relieving capacitance (CE 1 ;CE 2 ) is connected in parallel with each series diode (PS 1 ;DS 2 ).

What is claimed is:  
     
       1. A circuit arrangement having 
       a half-bridge arrangement comprising a first and a second switch (T 1 ;T 2 ), each switch (T 1 ;T 2 ) having, between its operating and reference electrodes, an internal diode (DB 1 ;DB 2 ), which is reverse-connected in parallel with the main current flow direction of the respective switch (T 1 ;T 2 ), and also an internal capacitance (C OSS   1 ;C OSS   2 ) a series diode (DS 1 ;DS 2 ) being arranged in series with the respective switch (T 1 ;T 2 ) in the main current flow direction in such a way that current can flow in the main current flow direction, and a freewheeling diode (DF 1 ;DF 2 ) being connected in parallel with the respective series circuit formed by the switch (T 1 ;T 2 ) and the series diode (DS 1 ;DS 2 ), and  
       a load circuit (L;RL), which has at least one inductive component (L) and is connected to the midpoint of the half-bridge arrangement,  
       wherein a load-relieving capacitance (CE 1 ;CE 2 ) is connected in parallel with each series diode (DS 1 ;DS 2 ). 
     
     
       2. The circuit arrangement as claimed in claim  1 , wherein the first and second switches (T 1 ;T 2 ) of the half-bridge arrangement are realized by a MOSFET, the respective internal diode being formed by the respective body diode (DB 1 ;DB 2 ) and the respective internal capacitance being formed by the respective output capacitance (C OSS   1 ;C OSS   2 ). 
     
     
       3. The circuit arrangement as claimed in claim  1 , wherein each load-relieving capacitance (CE 1 ;CE 2 ) is dimensioned in such a way that the voltage dropped during operation of the circuit arrangement across the load-relieving capacitance (CE 1 ;CE 2 ) of the respective voltage divider essentially formed from the load-relieving capacitance (CE 1 ;CE 2 ) and the internal capacitance (C OSS   1 ;C OSS   2 ) is always smaller than the reverse voltage of the respective series diode (DS 1 ;DS 2 ). 
     
     
       4. The circuit arrangement as claimed in claim  3 , wherein the load-relieving capacitance (CE 1 ;CE 2 ) is between 100 pF and 10 nF. 
     
     
       5. The circuit arrangement as claimed in claim  1 , wherein the half-bridge arrangement and two further switches form a full-bridge arrangement between whose midpoints the load circuit (L;RL) is coupled. 
     
     
       6. The circuit arrangement as claimed in claim  1 , wherein the half-bridge arrangement and four further switches form a three-phase bridge to which the load is coupled. 
     
     
       7. A step-down controller having a circuit arrangement as claimed in claim  1 . 
     
     
       8. A DC motor power converter having a circuit arrangement as claimed in claim  1 . 
     
     
       9. A three-phase motor power converter having a circuit arrangement as claimed in claim  1 . 
     
     
       10. A ballast for operating discharge lamps having a step-down controller as claimed in claim  7 .